bims-mecosi 2025-09-14 papers

Issue of 2025–09–14
three papers selected by
Verena Kohler, Umeå University

Cold Spring Harb Perspect Biol. 2025 Sep 09. pii: a041765. [Epub ahead of print]

Ca2+ Fluxes across Membrane Contact Sites.

Lucia Barazzuol, Marisa Brini, Tito Calì.

The calcium ion (Ca2+) is a pivotal second messenger orchestrating diverse cellular functions, including metabolism, signaling, and apoptosis. Membrane contact sites (MCSs) are critical hubs for Ca2+ exchange, enabling rapid and localized signaling across cell compartments. Well-characterized interfaces, such as those between the endoplasmic reticulum (ER) and mitochondria and ER-plasma membrane (PM), mediate Ca2+ flux through specialized channels. Less understood, yet significant, contacts involving Golgi, lysosomes, peroxisomes, and the nucleus further expand the landscape of intracellular Ca2+ signaling. These organelles are engaged in Ca2+ homeostasis mainly through their MCS, but the molecular players and the mechanisms regulating the process of Ca2+ transfer remain incompletely elucidated. This review provides a comprehensive overview of Ca2+ signaling across diverse MCS, emphasizing understudied organelles and the need for further investigation to uncover novel therapeutic opportunities.

DOI: https://doi.org/10.1101/cshperspect.a041765

Contact (Thousand Oaks). 2025 Jan-Dec;8:8 25152564251376890

Pseudomonas syringae HopN1 Binds Plant VAP12 and a Rho-GTPase, Suggesting a Role in Membrane-Associated Processes.

Charlotte Brinkmann, Jennifer Bortlik, Frederik Börnke.

Many Gram-negative bacterial pathogens deploy type III effector proteins (T3Es) to manipulate host cellular processes and suppress immune responses. Increasing evidence suggests that certain T3Es mimic eukaryotic FFAT (two phenylalanines in an acidic tract) motifs, enabling interaction with vesicle-associated membrane protein (VAMP)-associated proteins (VAPs). These interactions likely help pathogens target and exploit host membrane contact sites. However, the significance and distribution of FFAT mimicry across different bacterial pathogens remain poorly understood, which is crucial to uncovering its role in pathogenic strategies. In this study, we analyzed the T3E repertoire of the model plant pathogenic bacterium Pseudomonas syringae pv. tomato (Pst) DC3000 to identify potential FFAT motifs. Our preliminary data reveal that HopN1, a Pst T3E belonging to the YopT/AvrPphB family of cysteine proteases, contains at least one functional FFAT motif. Yeast two-hybrid and in planta co-immunoprecipitation assays confirmed that HopN1 interacts with plant VAP proteins. This interaction suggests that VAP binding may facilitate its localization to specific membrane compartments. Furthermore, HopN1 was shown to interact with a plant RHO-GTPase, hinting at a functional parallel to YopT in mammals. Our findings demonstrate that HopN1 interacts with VAP12 and a plant RHO-GTPase, suggesting a potential role in membrane-associated processes. However, whether HopN1 actively exploits VAP proteins for subcellular localization remains to be determined. While FFAT motif mimicry may contribute to effector targeting in plant-pathogenic bacteria, further studies are required to establish its functional significance in HopN1 virulence.

Keywords: FFAT-motif; HopN1; VAP proteins; plant defense; pseudomonas; type-III effector

DOI: https://doi.org/10.1177/25152564251376890

Acta Neuropathol Commun. 2025 Sep 10. 13(1): 190

Stabilizing the retromer complex rescues synaptic dysfunction and endosomal trafficking deficits in an Alzheimer's disease mouse model.

David Ramonet, Anna Daerr, Martin Hallbeck.

Disruptions in synaptic transmission and plasticity are early hallmarks of Alzheimer's disease (AD). Endosomal trafficking, mediated by the retromer complex, is essential for intracellular protein sorting, including the regulation of amyloid precursor protein (APP) processing. The VPS35 subunit, a key cargo-recognition component of the retromer, has been implicated in neurodegenerative diseases, with mutations such as L625P linked to early-onset AD. Despite growing evidence for retromer dysfunction in AD, its role in synaptic pathology and neuroinflammation remains incompletely understood. Here, we investigate the acute molecular effects of retromer stabilization in the 5xFAD mouse model of AD using the pharmacological chaperones R55 and R33, previously identified to enhance VPS35 stability. Following intracranial stereotaxic injections, we performed transcriptomic profiling, quantitative histology, and immunohistochemistry to assess synaptic function, neuroinflammation, and endosomal trafficking. Our findings reveal that retromer stabilization reverses multiple AD-associated molecular changes. R55 treatment significantly reduced Aβ-related pathology, normalized synaptic gene expression, and restored long-term potentiation (LTP)-associated pathways, including Gria1 (AMPA receptors), Grip1, and semaphorin/plexin signaling. Additionally, retromer stabilization counteracted dysregulated calcium signaling by modulating Ryr2 and L-type calcium channel expression. Beyond synaptic effects, we observed broad transcriptional and structural changes in the endosomal system. Notably, R55 treatment decreased VPS13 family gene expression, implicated in membrane contact site regulation, while increasing RAB7 levels, suggesting enhanced late-endosomal recycling. VPS35-positive vesicles were redistributed away from the nucleus, indicating restored intracellular trafficking dynamics. In the neuroinflammatory domain, retromer stabilization modulated microglial activation, shifting towards a profile characterized by balanced pro-inflammatory (Il1, Nfkb2) and anti-inflammatory (Il4r, Il13ra1, Stat6) markers, consistent with disease-associated microglia (DAM) phenotypes. Together, these findings demonstrate that retromer dysfunction contributes to key AD pathologies, including synaptic dysfunction and neuroinflammation, and that pharmacological retromer stabilization can restore cellular homeostasis. Given that 5xFAD mice lack direct VPS35 mutations, our results suggest that retromer-targeting strategies may be applicable to both familial and sporadic AD, offering a promising therapeutic avenue for modifying disease progression.

DOI: https://doi.org/10.1186/s40478-025-02096-8